We talked to experts on aging about the 2020 field. Here’s what they told us.

Joe Biden was lying on the operating table and about to get surgery for his second brain aneurysm when the doctor told him he might not recover.

“What's the most likely thing that will happen if I live?” Biden asked him. “Well,” the doctor replied, “the side of the brain that the first aneurysm is on controls your ability to speak.”

That’s when the gaffe-prone Biden thought to himself: “Why in the hell didn’t they tell me this before the '88 campaign?’ It could’ve saved us all a lot of trouble, you know what I mean?”

That joke, which Biden told in a speech in 2013, has taken on new relevance now that he’s on the campaign trail for president again and facing questions about his gaffes. Though Biden has a longstanding reputation for verbal flubs, they’re now inextricably linked to the 76-year-old’s age.

But concerns about Biden’s age and mental fitness are likely overblown, according to experts on aging and the brain, as well as actuarial tables used by the insurance industry to estimate the health and longevity of customers.

The two brain aneurysms Biden suffered in 1988 were fully treated and he showed no signs of mental trouble as a result, said Dr. Neal Kassell, who performed the surgery on Biden three decades ago. Nor did Biden suffer any brain damage that could come back to haunt him in old age, Kassell said.

“He is every bit as sharp as he was 31 years ago. I haven’t seen any change,” Kassell said. “I can tell you with absolute certainty that he had no brain damage, either from the hemorrhage or from the operations that he had. There was no damage whatsoever.”

Biden isn’t the only presidential candidate facing questions about age — five of them are 70 or older, including 73-year-old Donald Trump — but there's reason not to fret about the others, either.

The oldest candidate, Bernie Sanders, will turn 78 next month — eclipsing the average life expectancy for a man in the United States by two years. The youngest of the septuagenarian candidates is Elizabeth Warren, 70. Trump’s little-known Republican challenger, former Massachusetts Gov. Bill Weld, is 74.

With the prospect that the next president might be the oldest ever to take office, a team of researchers with the American Federation for Aging Research released a study last month to answer this morbid question: How likely is he or she to die in office?

The answer: Not very.

The candidates “have prospects for survival that extend well beyond the four-year term of the office. The bottom line is their chronological age does not matter at all,” Dr. S. Jay Olshansky, who led the study, said.

Of course the researchers can't predict death: Their life-expectancy projections for the candidates are based on estimates of the entire population contained in actuarial tables used by the insurance industry and the Social Security Administration. There’s no better way to estimate the longevity or health of the candidates without individual medical examinations and a look at their medical records, they said.

But “there was nothing we could see that would lead us to believe that the age of an individual, in and of itself, should be a disqualifying factor to run for president,” Olshansky said.

For someone of Sanders' age and gender, the study pegs the chances of surviving a four-year term at 76.8 percent. The corresponding figures for the other candidates are Biden at 79.2 percent, Weld at 83.6 percent, Trump at 84.8 percent and Warren at 91.8 percent.

But Olshansky points out that presidential candidates are probably healthier than the average U.S. citizen — and will likely live longer than the average as a result. People who have good health care, are more highly educated and have pensions generally live longer.

“They all belong to a subgroup of the population that is privileged. And privileged subgroups tend to live longer and better than the average,” Olshansky said. “Despite Bernie Sanders perhaps claiming otherwise, he’s part of the 1 percent. Actually, it’s more like 1/100 of 1 percent.”

Olshansky said the older candidates could belong to a group of what are called “superagers,” people who live into their 80s but show a mental sharpness as if they were in their 50s or 60s.

As for Biden’s prior brain surgeries, Rogalski said she can’t comment because she hasn’t evaluated him.

“It’s difficult to comment specifically on any one individual’s cognitive status without knowing more deeply about their medical history,” she said.

Olshansky echoed her point and said it was also “inappropriate” for psychologists and psychiatrists to opine on Trump's mental acuity without having analyzed him. And, he said, it’s a stretch to make candidates' gaffes into something more than understandable human error.

“When you hear somebody on TV and they make a mistake during a speech or a debate, you’ve got to cut them some slack,” Olshansky said. “If you’ve ever given a speech, it’s not easy standing in front of a crowd of people — especially standing in front of television cameras with millions of people watching — and avoiding verbal mistakes.”

Biden’s physician, Dr. Kevin O'Connor, said in a statement provided by the campaign that “Vice President Biden is in excellent physical condition. He is more than capable of handling the rigors of the campaign and the office for which he is running.”

Kassell, who performed brain surgery on Biden, went a step further: “I am going to vote for the candidate who I am absolutely certain has a brain that is functioning. And that narrows it down exactly to one.”

Though some theorize that the presidency ages office-holders more than the average adult, a 2011 study by Olshansky showed that wasn’t the case. Of 34 presidents who died of natural causes, 23 lived longer than expected, based on actuarial data.

Though the high number of older candidates is new in the 2020 election cycle, the politics of age and morbidity on the campaign trail isn’t.

In 2008, for instance, when Biden was running on Barack Obama’s ticket, the campaign indirectly attacked Republican nominee John McCain’s age by noting his running mate, Sarah Palin, was “a heartbeat away from the presidency.” At the time, McCain had a 1 in 3 chance of not living to age 80. He died just short of his 82nd birthday and would have completed both terms of his presidency had he won in 2008 and been reelected in 2012.

Hal Tepfer, a professor of actuarial sciences at Boston University, cautioned against relying too much on actuarial estimates for the presidential candidates, whose lifestyles and education probably make them more likely to live longer than the average American.

Regardless, Tepfer said, they’re still septuagenarians. And there’s still a risk, whether it’s for voters choosing a president or an insurance industry accepting a customer.

“They’re still likelier to die than the average person,” he said. “That’s why they probably can’t buy insurance. If I’m 75, they’re not going to sell me long-term care insurance because they know I’m going to use it. The same is true for life insurance. Why would they issue a policy to a 77-year-old if he’s going to be dead soon and they know they’ll never get their money back?”

CORRECTION: An earlier version of this story misstated the chances John McCain would have had of living to age 80 at the time he ran for president in 2008.